1. Field of the Invention
The present invention relates to image coding system wherein a binary document image is subjected to compression coding to thereby manage the document image efficiently and high speed retrieval of the document image becomes possible.
2. Description of the Prior Art
FIG. 1 is a flow chart of an image coding system in the prior art (MH coding system, i.e., modified Huffman coding system), for example, disclosed in Japanese patent application laid-open No. 62-144282. In FIG. 1, numeral 911 designates a MH coding processing step where a first image 903 being original data, is subjected to MH coding and a compression data 904 is obtained, numeral 912 designates a MH decoding processing step where the compression data 904 is subjected to MH decoding back into the first image 903, and numeral 1000 designates a resolution conversion processing step where a thinned-out image 905 is obtained from the first image 903 subjected to MH decoding. The step 1000 continues to step 1001 in FIG. 2.
In FIG. 2, numeral 1001 designates a read step of compression codes, numeral 1002 designates a decision step of front of line, numeral 1003 designates a calculation processing step of picture element length, numeral 1004 designates a reduction processing step of the picture element length estimated in step 1003, numeral 1005 designates a generation processing step of the reduction image utilizing the picture element image generated in step 1004, numeral 1006 designates a decision processing step of all lines at the front of line, numeral 1007 designates a decision step of thinned-out line, and numeral 1008 designates a front retrieval processing step of next line in the case of the thinned-out line.
Next, operation will be described. In FIG. 1, the first image 903 is subjected to MH coding according to the MH coding processing step 911; thereby the compression data 904 is obtained. In order to obtain the first image 903 in next MH decoding, the compression data 904 is first decoded according to the MH decoding processing step 912. Also in order to obtain the thinned-out image 905, in addition to the MH decoding, resolution conversion processing must be performed according to step 1000 as hereinafter described referring to FIG. 2.
In FIG. 2, decision of front of line is first performed by the code data read according to the read step 1001 of compression code (step 1002). As a result, if the code is not front of line, the picture element length is calculated (step 1003), and then reduction of the picture element length is performed (step 1004) thereby the reduction image is generated (step 1005). On the other hand, in the case of the front of line being determined in step 1002, decision is performed as to whether all lines come to the end (step 1006). If it is the end, the processing comes to the end, and if it is not the end, decision of thinned-out line is performed (step 1007). If it is thinned-out line, front retrieval of next line is performed (step 1008) and the processing is returned to step 1001.
Since the image coding system in the prior art is constituted as above described, even when the content of a document image is viewed using a display device with low resolution, all data must be read. Further, since the image for retrieval must be estimated by resolution conversion processing, high speed operation is difficult in such a system.